Good approach to make planks for a barrel?
There undoubtedly lots of ways of doing this. Here's one of them:

Array modifier

Use an array modifier with an object offset to duplicate one board object around radially. This way all the boards can be easily tweaked later on by editing just one; changes will be copied to the other boards.


Create the board object. If you want a certain number of boards (say, 16), then you'll want to be sure the board's width is 1 16th the circumference of the desired circle. The easiest way to do this is add a circle with 16 sides:




Add a circle (&#8679; ShiftA) and set the sides to 16 in the redo panel.
Extrude (E) it into a barrel shape. I used a loop cut (&#9096; CtrlR), beveling (&#9096; CtrlB), and scaling (S) to quickly make a basic barrel shape.
Select one face loop (&#9095; Alt RMB) and invert the selection (&#9096; CtrlI), then delete faces (&#8998; Delete, F)
With the remaining face loop selected, extrude (E) and press Esc to cancel the transform. Scale along the normals (&#9095; AltS) to give the board some thickness.

Setup the array modifier




Add an empty and rotate it 360/16 degrees (R, = 360/16 will do the math in place and rotate the empty 22.5&deg;)
with the board selected, add an array modifier, disable Relative Offset, and set the Count to 16.
Set the empty as the Object Offset. 

Optionally fatten up the board object (&#9095; AltS in edit mode) to reduce the size of the cracks between the boards.


Result: